Sept. 6, 2011 -- Babesiosis, a potentially life-threatening tick-borne disease, is an uncommon but serious complication of blood transfusions, according to a CDC report.

The report is published in the Annals of Internal Medicine. It documents cases of transfusion-related babesiosis reported over the past three decades.

"It's uncommon but important and a high priority," says the CDC's Barbara Herwaldt, MD, lead author of the report. However, she says, "People should not be afraid of transfusions. ...The blood supply is not unsafe."

In the U.S., babesiosis is caused by two species of parasite: Babesia microti (B. microti) and Babesia duncani (B. duncani). Most people get the disease from Ixodes scapularis ticks (also called blacklegged or deer ticks) that are common in the Northeast and upper Midwest. Because contaminated blood can be transported anywhere in the country, a few transfusion-related cases have been reported outside the hot spots where the disease usually occurs.

Symptoms of Babesiosis

The symptoms of babesiosis usually appear one to four weeks after infection, but can come much later. They resemble flu symptoms and often include fever, headaches and muscle aches, sweating, fatigue, nausea and vomiting, and weakness.

Babesiosis can also cause a type of anemia known as hemolytic anemia.

Many people with the disease, which is treated with antibiotics, have no symptoms. However, for certain groups, babesiosis can be severe or, in some cases, deadly, causing kidney and liver failure as well as dangerous heart and lung problems.

According to the CDC, people at the highest risk include those without a spleen or whose spleen functions abnormally, as well as those with compromised immune systems or who have other serious health problems, such as kidney or liver disease. Infants and the elderly are also susceptible to the disease's more dangerous symptoms.

The first known case of babesiosis transmitted via a blood transfusion occurred in 1979. In the decades since, more than 160 cases have been documented, most of them in the last 10 years, according to the CDC report. However, it is unclear whether the disease is becoming more prevalent or whether growing awareness about the disease has led to more diagnoses. That, Herwaldt says, is an important distinction.

"With increasing awareness, there may be an upsurge in the number of cases reported," she says, "but that does not necessarily reflect more risk."

Development of a Screening Test

Although most cases are caused by ticks, babesiosis can occur following a blood transfusion if the donor was infected. People with a history of babesiosis are not allowed to donate blood. Because symptoms of the disease can be mild to nonexistent, some donors are unaware that they have had the disease.

Currently, there is no FDA-approved tool to screen blood donors for babesiosis. That may change within the next few years.

"We are working with companies to try to help them get an FDA-approved test," says Richard Benjamin, MD, PhD. Benjamin is the chief medical officer of the American Red Cross Biomedical Services. He was not involved in the CDC report. "This paper is one way to get industry more focused on this issue."

Benjamin echoes Herwaldt's concerns about the significance of the problem. He says the report makes clear that the extent of known cases had been previously underreported.

"The big surprise in the paper is the numbers," he says. "Previously, if you'd asked me, I would have said 70 to 100. The report documents about twice as many."

The actual number of cases that occur in a given year is unknown. The disease, even in cases that cause severe symptoms, are often missed or misdiagnosed. As Herwaldt and her colleagues write, the 162 cases in the report "undoubtedly represent a fraction of those that occurred."

"Sufficient cases have been documented to demand a response," Benjamin says.

"If you have a medical condition that requires a blood transfusion," he says. "I would not be afraid. This is not HIV."